The present invention relates in general to pressure transducers and is concerned, more particularly, with a new and improved fluid-filled, direct-sensing pressure transducer. Even more particularly, the present invention relates to pressure transducer constructions that may be adapted for both mid-range and high pressure range measurements. The mid-range pressures are typically 1500-7500 psi and the high range pressures are typically 7500-50,000 psi. Moreover, the present invention relates to an improved method of forming the pressure transducer and in particular of interconnecting the transducer sensing element and capillary tube.
The following is a list of prior art patents that in general relate to pressure transducers: U.S. Pat. Nos. 3,349,623, 4,369,659, 3,678,753, 3,349,623, 2,940,313, 2,627,749, 2,326,047, 3,336,555, 2,738,677. Some of these patents are owned by the assignee herein and show fluid filled pressure transducers.
U.S. Pat. Nos. 2,949,313 and 2,627,749 both illustrate pressure indicators that employ strain tubes or the like for transmitting pressure to a diaphragm on which pressure is sensed by strain gages.
U.S. Pat. Nos. 3,326,047 and 3,336,555 illustrate pressure transducers. U.S. Pat. No. 3,336,555 illustrates an unfilled pressure transducer with strain gage sensing. U.S. Pat. No. 3,326,047 on the other hand illustrates a fluid filled pressure transducer employing a pressure sensing capsule having inner and outer deformable cylindrical walls. The liquid-filling in a transducer of this type has a relatively large volume and thus creates limitations upon the range of pressure measurements.
U.S. Pat. No. 2,738,677 is actually directed to a pressure indicator particularly for combustion chambers such as in an internal combustion engine.
Liquid-filled pressure transducers owned by the assignee herein include U.S. Pat. Nos. 3,349,623; 3,678,753; and 4,369,659. The early U.S. Pat. No. 3,349,623 describes a device employing an annular sensing chamber with associated strain gages. U.S. Pat. No. 3,678,753 is believed to be an improved form of the earlier version employing a top cap member and associated disc-shaped compartment defined between the cap member and the body of the instrument. The transducer illustrated in U.S. Pat. No. 3,678,753 provided an increased operating pressure range. U.S. Pat. No. 4,369,659 describes a melt pressure transducer preferably for use in pressure measurements associated with an injection molding machine and employing a novel temperature compensating filler rod.
Another prior art patent is U.S. Pat. No. 3,128,628 to Lebow. This patent illustrates a pressure transducer but does not employ any capillary tube.
In all of the prior art, referred to hereinbefore one of the main limitations, is the inability to operate particularly at high pressure levels such as in a pressure range of 10,000-50,000 psi.
Accordingly, one important object of the present invention is to provide a liquid-filled pressure transducer operating at high pressure ranges.
Another object of the present invention is to provide an improved pressure transducer that is fluid-filled and that employs a reduced volume of fluid. This reduced volume of fluid provides for minimization of temperature effects upon pressure and furthermore makes for improved diaphragm constructions.
Accordingly, a further object of the present invention is to provide an improved liquid-filled pressure transducer in which diaphragm stresses are reduced.
Still another object of the present invention is to provide an improved fluid-filled pressure transducer that provides for reduced snout diaphragm stresses during applied pressure and upon exposure to elevated temperature.
Still another object of the present invention is to provide an improved fluid-filled pressure transducer provided with a snout piece of a different material, provided for the purpose of temperature compensation and for improving overall performance. The snout piece permits the liquid-filled void to expand at the same rate as the liquid itself during temperature changes.
A further object of the present invention is to provide an improved method of construction of a liquid-filled pressure transducer, particularly an improved technique for interconnecting the sensing element and capillary tube of the pressure transducer.